Transcription signals in a region essential for replication of plasmid R6K.

A DNA fragment encoding for the enzyme chloramphenicol acetyltransferase (CAT) but lacking the CAT promoter sequence was used to probe transcription signals in a DNA fragment (640 base pairs) from plasmid R6K that plays a central role in R6K DNA replication. The R6K DNA fragment analyzed contains the seven 22-bp direct repeats which express R6K incompatibility and are required in cis for activity of all three of the R6K origins of replication. In addition to the previously identified promoter sequences for the R6K initiation protein pi (P pi), a relatively weak transcriptional promoter upstream to P pi was detected. On the opposite strand an efficient (94%) transcriptional terminator was identified. This terminator is located upstream to nucleotide sequences active in the repression of R6K DNA replication.